October 24, 2012
Low Genetic Diversity Spells Bad News For Koalas
Brett Smith for redOrbit.com - Your Universe Online
When populations of animals are under threat, a major concern surrounding their potential for survival is the genetic diversity within the population. A high level of genetic diversity makes for a resilient population, while low genetic diversity could be a red flag for conservationists.
In a new study, an international team of researchers has investigated the genetic diversity of the koala population and found through both historical and modern samples that the species has had a relatively low level of diversity for the past 120 years.
According to their report in the open access journal BMC Genetics, the researchers from the European Union and the United States sequenced the mitochondrial DNA (mtDNA) of 14 museum specimens to track the historical genetic diversity of koalas and compare those results to the sizes of the population that each historical sample belonged to when it was killed. They also sequenced the mtDNA of koalas currently living in Eastern Australia.
They found that the historical mtDNA of koalas only contained four different haplotypes that could be used to genetically differentiate individuals, and all of these haplotypes exist in modern koalas.
These results led the scientists to believe that the koala population was stripped of its diversity before any of the historical samples existed–over 120 years ago. They also may explain the animal´s susceptibility to certain diseases like Chlamydia and the koala retrovirus.
"We thought that, like other species such as the grey wolf where the population has recently declined, there should be greater diversity in museum samples than modern specimens,” said Alex Greenwood, from the Leibniz-Institute for Zoo and Wildlife Research in Berlin. “We found this not to be true. The event which reduced the genetic diversity of koalas must have happened a long time ago, perhaps during the late Pleistocene when the larger species of koala, P. stirtoni, became extinct."
The researchers noted in their report that low genetic diversity does not necessarily mean inbreeding has occurred within the population and any management of conservation strategies should take this into account.
The koala population has been under stress for as long as they have been in contact with humans and possibly before that. When European explorers first encountered the koalas that were living alongside Australia´s aboriginal peoples in the late 18th century, they noted that their numbers were extremely low and they expected the species to become extinct.
However, hunting of the animals declined in the following years and the koala population was quite robust by the mid 19th century, the years just before the time span covered in the study.
As fur trade stepped up in the late 1800s, the koala population was decimated once again as millions were thought to have been killed during that time. Koalas were also being constrained by human settlements that began encroaching on their territory at that time.
Unfortunately, the koala population isn´t the only Australian species to experience low genetic diversity throughout recent history. Previous research has shown that the Tasmanian devil also has a historically low genetic diversity over the past 120 years.